1. Field of the Invention
The present invention relates generally to implantable cardiac stimulation devices and systems for regulating the contraction of a heart. More particularity, the invention relates to a defibrillation lead, and more particularly to a defibrillation lead having a steerable distal end.
2. Description of the Related Art
Implantable medical devices for treating irregular contractions of the heart with electrical stimuli are well known in the art. Some of the most common forms of such implantable devices are defibrillators and pacemakers.
Defibrillators are implantable medical devices used to treat fibrillation, a condition characterized by rapid, chaotic electrical and mechanical activity of the heart""s excitable myocardial tissue that results in an instantaneous cessation of blood flow from the heart. Defibrillation is a technique employed to terminate fibrillation by applying one or more high energy electrical pulses to the heart in an effort to overwhelm the chaotic contractions of individual tissue sections and to restore the normal synchronized contraction of the total mass of tissue.
A pacemaker, or pacer, is an implantable medical device that delivers low energy electrical pulses to stimulate a patient""s heart to beat at a desired rate in instances where the heart itself is incapable of proper self-regulation. This occurs when the heart""s natural pacemaker, which causes the rhythmic electrical excitation of the heart and pumping of blood, malfunctions due to age or disease. Demand pacing is a process used to maintain normal beating of a heart having this condition.
Various types of leads for defibrillators and demand pacers have been suggested in the prior art. For example, large electrical patches sewn to the exterior surface of the heart have been used to deliver defibrillation pulses to the heart. Implantation of such patch electrodes requires opening of the patients chest during thoracic surgery. For pacing, pulses may be applied to the heart with the use of a pacer lead having an exposed metal surface, or demand pacer electrode, extending through a vein and into the heart.
Those involved in the medical arts recognized that prior art defibrillators required a high threshold level of energy for effective defibrillation, which limited the useful life-span of the devices and, more significantly, posed a significant risk of causing electrolysis of the blood and myocardial damage. It was realized that the defibrillation electrode configuration played an important role in the amount of energy needed to achieve successful defibrillation. This led to the development of transvenous defibrillation leads having long coil-shaped defibrillation electrodes for implantation into the right ventricle of the heart through a vein. For example, U.S. Pat. No. 4,922,927, the entire disclosure of which is incorporated herein by reference, discloses a defibrillation electrode made up of a plurality of separate wires wound side-by-side to form a tight coil. The coil was disposed upon an insulated tubular member and had a length sufficient to extend throughout the entire length of the ventricular chamber to provide sufficient electrode surface area for defibrillation.
Transvenous cardiac stimulation leads, such as the device of U.S. Pat. No. 4,922,927, also carry a demand pacing electrode. Thus, a single device implantable in one surgical procedure could provide defibrillation and pacing pulses for heart patients suffering from both irregular heart beat and, at times, cardiac fibrillation. This eliminated the need for multiple and complex surgical procedures to attach electrodes for both types of treatments.
Another defibrillation electrode configuration for use with dual purpose transvenous leads is disclosed in U.S. Pat. Nos. 5,476,502 and 5,374,287 to Rubin, which are also incorporated herein by reference in their entireties. The xe2x80x9cRubinxe2x80x9d catheter included either a helical or lance shaped defibrillation electrode for delivering a defibrillation pulse directly to the interior of the septum of the patient""s heart. The length of the helix-shaped electrode to be screwed into the septum from the right ventricle, about 0.5 cm to 1.0 cm, was substantially shorter than the conventional coiled transvenous defibrillation electrodes.
The characteristics and advantages of the present invention described above, as well as additional features and benefits, will be readily apparent to those skilled in the art upon reading the following detailed description and referring to the accompanying drawings.
We have invented a defibrillation lead with steerable characteristics, allowing the lead to be more easily placed within the coronary sinus. The lead of our invention comprises an elongated lead body having a proximal end and a distal end. At the proximal end there is an electrical connector. Adjacent the distal end, there is an electrode, preferably a coiled defibrillation electrode placed on the exterior of the elongated lead body. The distal end of the lead body has a permanent set or bend. A torque tube, extending through a lumen in the lead body from the proximal end of the lead to an anchor block adjacent the distal end of the lead, can be rotated by a physician to orient the bend in the lead. A cable passes through the torque tube from the proximal end of the lead through the anchor block to the distal end of the lead. This cable is affixed to a wall of the lumen, preferably in the direction of the bend. Pulling on the cable temporarily changes the bend in the distal end of the lead.
An important object of our invention is to provide a lead that can be directed into the coronary sinus of the heart.
Another important object of our invention is to provide a defibrillation lead which can be directed into the coronary sinus, using a bent distal end.
Another object of our invention is to provide a coronary sinus lead wherein the radial orientation of a bent distal lead can be controlled.
It is also an object of our invention to provide a lead having a torque apparatus for controlling the orientation of the distal of the lead. Another object of our invention is to provide the coronary sinus lead having a bent distal end wherein the degree of bending can be controlled.
These and other features and objects of our invention will be apparent to those skilled in the art from the following detailed description of our preferred embodiment, taking in connection with the accompanying drawings.